Self-energizing phaseshifters, which utilize the inherent bidirectional torque pulses in the valve train as the source of energy to shift the camshaft phase relationship relative to the engine crank rotation been proposed. For example U.S. Ser. No. 620,517, now U.S. Pat. No. 5,121,717, and U.S. Ser. No. 695,162, now U.S. Pat. No. 5,117,784, Internal Combustion Engine Camshaft Phaseshift Control Systems, and U.S. Ser. No. 856,268, now U.S. Pat. No. 5,165,368, Internal Combustion Engine With Variable Compression Ratio, all assigned to the Assignee of this invention, show devices for modular varying of the timing of the camshaft relative to the crankshaft, thus varying the timing of the engine valve actuation during engine operation.
This is accomplished through a low power consumption technique of self-actuating phaseshift wherein the overall engine performance is improved. Hydraulic control circuits control the onset and rate of phase change in the camshaft by controlling the oil flow between two oil volumes which are radially compressed to transfer motion from the engine to the camshaft.
These devices use the reaction torque pulses, induced by the compression and decompression of the engine valve return springs, as the energy for accomplishing the fluid flow between cavities and the resultant phaseshifting, which allows each system to be self-actuating with low power consumption, since no external hydraulic power is necessary to rotate the coupling between the camshaft and crankshaft.
In U.S. Ser. No. 856,272 now U.S. Pat. No. 5,163,386, Stroke/Clearance Volume Engine, also assigned to the Assignee of this invention, the reciprocating motion of the piston and rotation of the connecting rod produces auxiliary torque impulses acting first in one direction and then in the other as a function of the position of the piston. These torque pulses are used to cause a phaseshifting of the engine timing events to enhance fuel economy and reduce emissions, and for other reasons.
When the valve spring is compressed during opening of the valve, the rotation of the camshaft exerts a resistance to rotation of the crankshaft and therefore a positive torque is required to turn the camshaft. On the other hand, when the valve is being closed by the spring, the camshaft in effect is attempting to rotate ahead of the crankshaft, and a negative torque felt by the crankshaft develops to counteract this advancing torque of the camshaft.
In each of the above cases, it is important that the bidirectional torque pulses be approximately equal or symmetrical so that the forces applied in opposite directions to properly operate the phaseshifter will provide the desired phaseshifting. In some engines, the negative and positive torque pulses are not equal and there may be a substantial difference between them. These engines would not be suitable for use with the phaseshifters described above as self-energizing phaseshifters. In these engine installations, the bidirectional torque impulses may either cancel one another or are too weak to be effective as a phaseshifting force.
This lack of bidirectional torque pulses may be the result of two factors: 1) the manner in which torque reversals from individual cam lobes combine tends to cancel rather than enhance torque reversals due to the engine firing frequencies; and 2) negative torque swings as applied to the crankshaft, although adequate on their own to advance the phaseshifting mechanism, are removed due to positive torque on the crankshaft added due to bearing friction and/or accessory torque drag.
Stated another way, the greater the number of cams located on the camshaft, the denser the torque pulses become, i.e., the closer to one another they become. The entire camshaft experiences pulses originating in one direction from say one cylinder, whereas at the same time another cylinder is beginning to offset it, until it reaches a point where the phaseshifter is unable to recognize the origin, magnitude, or direction of the pulses, so that basically it loses the ability or speed with which changes can be made. The greater the torque pulse, the quicker the response and the quicker the phaseshift can be made.
Whatever the reason, a method and apparatus of enhancing the bidirectional torque pulses in one direction or the other would be needed to cause the self-energizing phaseshifter to be feasible. This invention provides such a bidirectional torque pulse enhancer concept.